The tweet from Mandel came two days after the ADL criticized activists and Internet personalities including Mike Cernovich and Jack Posobiec, according to The Hill.

The ADL named Cernovich, Posobiec and others to a list of people associated with the alt-right, a white nationalist movement that is mainly based on the Internet.

Cernovich and Posobiec pushed the "Pizzagate" conspiracy theory that alleged Hillary Clinton was involved in a child sex-trafficking ring in a Washington, D.C. pizza restaurant, according to the Hill.

The tweet from Mandel contained a retweet from Cernovich, who called the ADL list a "hit list of political opponents." He said with the list, the ADL is attempting to stir its supporters to kill those who disagree with the Jewish rights group, the Hill reported.